The present invention relates to a hydraulic brake system equipped with hydraulic brake force boosting. The system is substantially composed of a pedal-actuated master cylinder to which the wheel brakes are connected by way of pressure fluid lines of an auxiliary-pressure supply system, and of an auxiliary-pressure control valve which causes an auxiliary pressure proportional to the pedal force.
A known brake system of this type consists of a single-type or tandem-type master cylinder with a hydraulic brake power booster connected upstream thereof as well as of an auxiliary-pressure supply system comprising a pump and a hydraulic accumulator. The hydraulic booster contains an auxiliary-pressure control valve which, on actuation of the brake pedal, brings about an auxiliary pressure that is proportional to the pedal force and that acts on the pistons in the master cylinder. The boosting factor of the brake system is selected by the ratio of the surfaces of a transmission piston in the interior of the brake power booster in relation to the surface of an actuating piston coupled mechanically to the brake pedal. As the brake circuits are designed as static circuits, the volume of the pressure chambers in the master cylinders must be adapted to the respective brake system.
Furthermore, slip-controlled brake systems are known wherein the hydraulic braking pressure generator is likewise composed of a master cylinder and a hydraulic brake power booster connected upstream thereof, as disclosed in German printed and published patent applications Nos. 30 40 561 and 30 40 562. During slip control, dynamic pressure out of the auxiliary-pressure supply system is introduced by way of the booster chamber into the brake circuits which are connected to the master cylinder and which are static until commencement of slip control. This way, the discharge or pressure fluid into the pressure supply reservoir during the phases of pressure reduction will be compensated. Such systems are rather complicated and costly.
Likewise known are slip-controlled brake systems, the braking pressure generator of which is also composed of a hydraulic brake power booster with a master cylinder connected downstream thereof, and wherein on commencement of slip control dynamic pressure is metered out of the brake power booster directly into the wheel brake cylinders of the wheels connected to the master cylinder. To this end, the wheel brakes connected to the static brake circuit communicate by way of electromagnetically actuatable multidirectional control valves with the master cylinder so that change-over of these valves causes interruption of the hydraulic connection between the master cylinder and the wheel brakes and permits connection of the auxiliary-pressure source instead of the master cylinder. During normal braking operations (i.e., without slip control) or until change-over of the solenoid valves, respectively, the circuits concerned are strictly static brake circuits.
It is an object of the present invention to develop a brake system with hydraulic boosting which is comparatively simple and entails little effort and which system likewise permits to be extended to a slip-controlled brake system by insertion of electromagnetically controllable inlet and outlet valves and by equipment with a measuring and control electronics.